Diagnostic Analgesia Research Articles

A review of radiographic interpretation of the navicular bone

Navicular syndrome (also called navicular disease) plays a major role in the equine industry as a chronic, degenerative and often career-limiting disease process which affects a variety of breeds of horses. In addition to clinical signs and diagnostic analgesia, diagnostic imaging plays a key role in identification of this disease process – radiography is the most used imaging modality. In addition to their clinical utility, foot radiographs are a standard element of most pre-purchase examinations. Good radiographic quality and positioning are necessary for accurate interpretation. Radiographic lesions of the navicular bone such as sclerosis, enlarged synovial invaginations, distal border fragments and flexor cortical erosions are important to identify and understand because of their potential role in the disease process. This article reviews an approach to radiological evaluation and interpretation of lesions affecting the navicular bone.

Use of equine cadaver limb models to enhance veterinary student self-efficacy during arthrocentesis.

To determine if equine cadavers modified with joint distension would yield higher fluid volumes, require fewer needle redirects, and improve student self-efficacy. 19 third-year veterinary students. Voluntary participation was sought during 4 sessions of an equine arthrocentesis and diagnostic analgesia laboratory. Half of the sessions were provided with unmodified cadavers and half were provided with cadavers modified with joint distention. Prior to and after the laboratory, participating students completed surveys regarding their self-efficacy with arthrocentesis of the metacarpophalangeal and distal interphalangeal joints. During the study, the number of needle redirects and the volume of fluid obtained was recorded. Increased fluid volumes were obtained from the modified metacarpophalangeal and distal interphalangeal joints. No difference was identified in number of needle redirects between cadaver types for either joint. Self-efficacy scores increased at the end of the laboratory for arthrocentesis of the metacarpophalangeal joint in both modified and unmodified groups. Self-efficacy scores increased at the end of the laboratory for arthrocentesis of the distal interphalangeal joint for the modified but not unmodified groups. Modified equine cadavers provided a higher fluid yield following arthrocentesis compared to unmodified cadavers, but despite this, multiple attempts were required for proper needle placement. Performing equine arthrocentesis improved student self-efficacy with the task. Given our results, the model used for introduction to performing equine arthrocentesis may be less important than practice with the skill. In order to improve proficiency and self-efficacy, equine arthrocentesis should be provided multiple times throughout the veterinary curriculum.

Low-Field Magnetic Resonance Imaging Findings of the Fetlock Region of Nonracehorses

Low-field, magnetic resonance imaging (MRI) is an advanced imaging modality widely used to diagnose distal limb pathology in horses, but there are limited data regarding lesion distribution within the metacarpo/metatarsophalangeal joint (MCP/MTPJ) region in lame nonracehorses. The aim of this study was to describe the low-field MRI findings and lesion distribution in nonracehorses with MCP/MTPJ region pain. Clinical records from horses undergoing MRI of the MCP/MTPJ region between July 2016 and March 2023 were reviewed. Horses were included if pain causing lameness was localized to this region and conventional imaging failed to provide a definitive diagnosis. Eighty-four horses met the inclusion criteria. Soft tissues were affected in 76 (90.5%) horses, with suspensory ligament branch injuries being the most frequent (60.7%) soft tissue pathology identified. Osseous pathology was diagnosed in 51 horses. The subchondral bone (SCB) of the distal third metacarpal/metatarsal bone (MC3/MT3) was the osseous structure most frequently affected (40.5%), with 79.4% of these horses having lesions on the dorsal aspect of the bone. Osteoarthritis was present in 48 (57.1%) horses. The main limitations of the study were the lack of a standardized diagnostic analgesia pattern due to varying veterinary surgeon involvement, and the absence of bilateral magnetic resonance (MR) sequences in all limbs. MRI is a useful diagnostic tool to assess soft tissue structures in the MCP/MTP region, especially in horses with thick skin, which may make ultrasonographic imaging unreliable.

Validation of loss of skin sensation as an indicator of tibial nerve desensitisation following diagnostic perineural analgesia in lameness investigation

Validation of loss of skin sensation as an indicator of tibial nerve desensitisation following diagnostic perineural analgesia in lameness investigation

Objective evaluation for analgesia of the distal interphalangeal joint, the navicular bursa and perineural analgesia in horses with naturally occurring forelimb lameness localised to the foot.

The outcome and interpretation of intra-synovial diagnostic analgesia of the distal interphalangeal joint (DIPJ) and the navicular bursa (NB) remain in dispute, and no objective studies have been carried out to establish the percentage of improvement over time from these two analgesia techniques. To investigate the qualitative and time-dependent outcome of DIPJ-A and NB-A in naturally occurring forelimb lameness. Case series. Twenty-three clinical cases with forelimb lameness were evaluated objectively using a body mounted inertial sensor system (BMIS). Lameness was localised to the foot with a palmar digital nerve block and/or an abaxial sesamoidean nerve block on day 1, and analgesia of the DIPJ (DIPJ-A) and NB (NB-A) were performed on days 2 and 3. Improvement following perineural analgesia was measured after 10 min and intra-synovial blocks after 2-, 5- and 10-min. Horses with at least 70% improvement measured objectively after diagnostic analgesia were included in the study. There was no significant association between improvement following perineural analgesia and the DIPJ-A and NB-A. The mean improvement in the lameness differed between DIPJ-A and NB-A at 2 min (p < 0.001) and at 5 min (p=0.04), and it was no longer observed after 10 min (p=0.06). A positive NB-A produced a high degree of improvement that remained stable, whereas the DIPJ-A improved over time. Perineural and intra-synovial analgesia were performed without contrast medium to assess the diffusion of mepivacaine. Our results suggest that perineural analgesia is not reliable enough to differentiate pain originating from DIPJ and NB. Early evaluation of the DIPJ-A and NB-A can determine the origin of the pain. An improvement following NB-A was constant over time, but an improvement following DIPJ-A varied by up to 10 min.

Linear Discriminant Analysis for Investigating Differences in Upper Body Movement Symmetry in Horses before/after Diagnostic Analgesia in Relation to Expert Judgement.

Simple SummaryIdentifying the anatomical structures involved in causing pain and an associated lameness in a horse typically requires assessment in straight lines and circles and using regional administration of local anesthetic drugs (diagnostic analgesia). Visual assessment of changes in movement are affected by bias, i.e., expected changes influence decisions. Quantitative measurements with inertial sensors aim at removing this bias. The current study is aimed at investigating how a specific data-driven method, linear discriminant analysis (LDA), may be useful for aiding veterinary decision making about perceived changes in lameness. Changes in movement data after diagnostic analgesia and expert judgements from 53 lame horses were used to study (a) the accuracy of LDA-based decision making, (b) differences between straight-line and circular movement and (c) which commonly used movement features are most useful in this context. Accuracy was comparatively low and varied considerably between 36% and 57%, indicating considerable overlap between movement symmetry data of the diagnostic analgesia categories. The best data-driven separation between categories was observed when the limb in which perineural anaesthesia had been performed was on the inside of the circle (on hard ground for forelimb and on soft ground for hindlimb diagnostic analgesia). Movement features of all three landmarks (head, withers, pelvis) were important for data-driven classification, emphasizing the complexity of the movement pattern changes after diagnostic analgesia observed in lame horses.Diagnostic analgesia and lunging are parts of the equine lameness examination, aiding veterinarians in localizing the anatomical region(s) causing pain-related movement deficits. Expectation bias of visual assessment and complex movement asymmetry changes in lame horses on the lunge highlight the need to investigate data-driven approaches for optimally integrating quantitative gait data into veterinary decision-making to remove bias. A retrospective analysis was conducted with inertial sensor movement symmetry data before/after diagnostic analgesia relative to subjective judgement of efficacy of diagnostic analgesia in 53 horses. Horses were trotted on the straight and on the lunge. Linear discriminant analysis (LDA) applied to ten movement asymmetry features quantified the accuracy of classifying negative, partial and complete responses to diagnostic analgesia and investigated the influence of movement direction and surface type on the quality of the data-driven separation between diagnostic analgesia categories. The contribution of movement asymmetry features to decision-making was also studied. Leave-one-out classification accuracy varied considerably (38.3–57.4% for forelimb and 36.1–56.1% for hindlimb diagnostic analgesia). The highest inter-category distances (best separation) were found with the blocked limb on the inside of the circle, on hard ground for forelimb diagnostic analgesia and on soft ground for hindlimb diagnostic analgesia. These exercises deserve special attention when consulting quantitative gait data in lame horses. Head and pelvic upward movement and withers minimum differences were the features with the highest weighting within the first canonical LDA function across exercises and forelimb and hindlimb diagnostic analgesia. This highlights that movement changes after diagnostic analgesia affect the whole upper body. Classification accuracies based on quantitative movement asymmetry changes indicate considerable overlap between subjective diagnostic analgesia categories.

Visual lameness assessment in comparison to quantitative gait analysis data in horses.

Quantitative gait analysis offers objective information to support clinical decision-making during lameness workups including advantages in terms of documentation, communication, education, and avoidance of expectation bias. Nevertheless, hardly any data exist comparing outcome of subjective scoring with the output of objective gait analysis systems. To investigate between- and within-veterinarian agreement on primary lame limb and lameness grade, and to determine relationships between subjective lameness grade and quantitative data, focusing on differences between (1) veterinarians, (2) live vs video assessment, (3) baseline assessment vs assessment following diagnostic analgesia. Clinical observational study. Kinematic data were compared to subjective lameness assessment by clinicians with ≥8years of orthopaedic experience. Subjective assessments and kinematic data for baseline trot-ups and response to 48 diagnostic analgesia interventions in 23 cases were included. Between and within-veterinarian agreement was investigated using Cohen's Kappa (κ). Asymmetry parameters for kinematic data ('forelimb lame pattern', 'hindlimb lame pattern', 'overall symmetry', 'vector sum head', 'pelvic sum') were determined, and used as outcome variables in mixed models; explanatory variables were subjective lameness grade and its interaction with (1) veterinarian, (2) live or video evaluation and (3) baseline or diagnostic analgesia assessment. Agreement on lame limb between live and video assessment was 'good' between and within veterinarians (median κ=0.64 and κ=0.53). There was a positive correlation between subjective scoring and measured asymmetry. The relationship between lameness grade and objective asymmetry differed slightly between (1) veterinarians (for all combined parameters, p-values between P<.001 and 0.04), (2) between live and video assessments ('forelimb lame pattern', 'overall symmetry', both P≤.001), and (3) between baseline and diagnostic analgesia assessment (all combined parameters, between P<.001 and .007). Limited number of veterinarians (n=4) and cases (n=23), only straight-line soft surface data, different number of subjective assessments live vs from video. Overall, between- and within-veterinarian agreement on lame limb was 'good', whereas agreement on lameness grade was 'acceptable' to 'poor'. Quantitative data and subjective assessments correlated well, with minor though significant differences in the number of millimetres, equivalent to one lameness grade between veterinarians, and between assessment conditions. Differences between baseline assessment vs assessment following diagnostic analgesia suggest that addition of objective data can be beneficial to reduce expectation bias. The small differences between live and video assessments support the use of high-quality videos for documentation, communication, and education, thus, complementing objective gait analysis data.

Bone exostosis lesions in distal limb of equines (17 cases; 10 horses, 7 donkeys): A clinical study.

Lameness is an important clinical sign for the problems of locomotor system. When, visual inspection and diagnostic analgesia are not enough for reaching out the accurate diagnosis of the lesion, diagnostic imaging including radiology helps to determine the problem in a specific area. This study investigated the role of radiography as a crucial step for clinical diagnosis of bone exostosis lesions in equines. Between July 2019 and December 2020, seventeen animals were involved in this study 10 horses and 7 donkeys. These animals (age, 4.1±3.8 years; weight, 199±98 Kg) were suffered from lameness with prominent bone exostosis on the distal limb, then were subjected to radiographic examination with lateromedial and dorsopalmar/dorsoplantar views. The most detected cases were more prevalent in the fore limb (76.5%) than the hind limb (23.5%). The most prevalent lesions recorded in this study were ring bone (9 cases; 52.9%), Degenerative joint disease of the carpal joint and sore shins (3 cases; 17.64%) for each, and then bone spavin and side bone were the lowest prevalent one (1 case; 5.88%) for each. There was no treatment for all cases except sore shins which was improved thoroughly by topical iodine compounds with systemic administration of phenylbutazone. X-ray radiography is still beneficial for equine industry especially in the lesions related to the joints and bone exostosis that appeared on the distal limb.

Retrospective analysis of changes in upper body movement asymmetry after diagnostic analgesia in 149 horses undergoing clinical lameness examination accompanied by inertial sensor gait analysis

Retrospective analysis of changes in upper body movement asymmetry after diagnostic analgesia in 149 horses undergoing clinical lameness examination accompanied by inertial sensor gait analysis

Compensatory movement patterns of head, withers and pelvis following diagnostic analgesia on the straight and during lungeing on hard and soft surfaces

Compensatory movement patterns of head, withers and pelvis following diagnostic analgesia on the straight and during lungeing on hard and soft surfaces

Effect of Speed and Surface Type on Individual Rein and Combined Left-Right Circle Movement Asymmetry in Horses on the Lunge.

Differences in movement asymmetry between surfaces and with increasing speed increase the complexity of incorporating gait analysis measurements from lunging into clinical decision making. This observational study sets out to quantify by means of quantitative gait analysis the influence of surface and speed on individual-rein movement asymmetry measurements and their averages across reins (average-rein measurements). Head, withers, and pelvic movement asymmetry was quantified in 27 horses, identified previously as presenting with considerable movement asymmetries on the straight, during trot in hand and on the lunge on two surfaces at two speeds. Mixed linear models (p < 0.05) with horse as the random factor and surface and speed category (and direction) as fixed factors analyzed the effects on 11 individual-rein and average-rein asymmetry measures. Limits of agreement quantified differences between individual-rein and average-rein measurements. A higher number of individual-rein asymmetry variables—particularly when the limb that contributed to movement asymmetry on the straight was on the inside of the circle—were affected by speed (nine variables, all p ≤ 0.047) and surface (three variables, all p ≤ 0.037) compared with average-rein asymmetry variables (two for speed, all p ≤ 0.003; two for surface, all p ≤ 0.046). Six variables were significantly different between straight-line and average-rein assessments (all p ≤ 0.031), and asymmetry values were smaller for average-rein assessments. Limits of agreement bias varied between +0.4 and +4.0 mm with standard deviations between 3.2 and 12.9 mm. Fewer average-rein variables were affected by speed highlighting the benefit of comparing left and right rein measurements. Only one asymmetry variable showed a surface difference for individual-rein and average-rein data, emphasizing the benefit of assessing surface differences on each rein individually. Variability in straight-line vs. average-rein measurements across horses and exercise conditions highlight the potential for average-rein measurements during the diagnostic process; further studies after diagnostic analgesia are needed.

Movement asymmetries in horses presented for prepurchase or lameness examination.

SummaryBackgroundThe increasing popularity of objective gait analysis makes application in prepurchase examinations (PPE) a logical next step. Therefore, there is a need to have more understanding of asymmetry during a PPE in horses described on clinical evaluation as subtly lame.ObjectivesThe objective of this study is to objectively compare asymmetry in horses raising minor vet concerns in a PPE and in horses raising major vet concerns with that found in horses presented with subtle single‐limb lameness, and to investigate the effect of age/discipline on the clinicians' interpretation of asymmetry on the classification of minor vet concerns in a PPE.Study DesignClinical case‐series.MethodsHorses presented for PPE (n = 98) or subjectively evaluated as single limb low‐grade (1–2/5) lame (n = 24, 13 forelimb lame, 11 hindlimb lame), from the patient population of a single clinic, were enrolled in the study provided that owners were willing to participate. Horses undergoing PPE were assigned a classification of having minor vet concerns (n = 84) or major vet concerns (n = 14) based on findings during the dynamic‐orthopaedic part of the PPE. Lame horses were only included if pain‐related lameness was confirmed by an objective improvement after diagnostic analgesia exceeding daily variation determined for equine symmetry parameters using optical motion capture. Clinical evaluation was performed by six different clinicians, each with ≥8 years of equine orthopaedic experience. Vertical movement symmetry was measured using optical motion capture, simultaneously with the orthopaedic examination. Data were analysed using previously described parameters and mixed model analysis and least squares means were used to calculate differences between groups.ResultsThere was no effect of age or discipline on the levels of asymmetry within PPE horses raising minor vet concerns. MinDiff and RUD of the head discriminated between forelimb lame and PPE horses raising minor vet concerns; MinDiff, MaxDiff, RUD of the Pelvis, HHDswing and HHDstance did so for hindlimb lameness. Two lameness patterns differentiated both forelimb and hindlimb lame from PPE horses with minor vet concerns: RUD Poll + MinDiff Withers – RUD Pelvis and RUD Pelvis + RUD Poll − MinDiff Withers. Correcting for vertical range of motion enabled differentiation of PPE horses with minor vet concerns from PPE horses with major vet concerns.Main LimitationsObjective data only based on trot on soft surface, limited number of PPE horses with major vet concerns.ConclusionsCombinations of kinematic parameters discriminate between PPE horses with minor vet concerns and subtly lame horses, though overlap exists.

Interpretation of distal limb nerve blocks in the horse

Diagnostic analgesia of the distal limb is frequently performed in equine practice to localise lameness. The specificity of blocks has been widely investigated and it is important that clinicians understand the established blocking patterns and limitations for these blocks in order to correctly advise clients on diagnosis, further imaging and prognosis. This article examines the evidence relating to interpretation of distal limb blocks.

Retrospective analysis of oblique and straight distal sesamoidean ligament desmitis in 52 horses.

Injuries to the oblique (ODSL) or straight (SDSL) distal sesamoidean ligaments are a recognised cause of distal limb lameness in the horse. However, there are only limited publications addressing common diagnostic features and prognosis. (a) Report findings on ultrasonography and standing low-field magnetic resonance imaging (sMRI) in horses with ODSL or SDSL injury; (b) Identify clinical variables associated with lesion type and (c) Identify factors associated with return to soundness in horses with ODSL or SDSL injury. Retrospective case series. Horses with a primary diagnosis of ODSL or SDSL injury confirmed with a combination of diagnostic analgesia and detection of a lesion on imaging (ultrasonographic±advanced imaging) were included. Return to soundness and performance follow-up data were obtained. Fifty-one horses were included. SDSL injuries were more common in the forelimb (13/21, 62%), while ODSL injuries had equal frequency in fore- (15/30, 50%) and hindlimbs (15/30, 50%). ODSL injuries were more likely than SDSL injuries to affect the proximal third of the ligament (OR =13; 95% CI 2.3-74.3; p=0.004) and often presented with periligamentar swelling (20/30;67%) and focal pain (22/28;79%). Lesions were frequently detected using ultrasonography (35/42;83%) and sMRI examination (18/25;72%). Only 27/49 cases (55%) returned to soundness, with only 15/49 (31%) returning to intended use. There were no significant associations between outcome and clinical features or treatment. There was no comparative "gold standard" to validate lesions such as high-field MRI or histopathology. In contrast to previous studies, ODSL and SDSL injuries were readily identified ultrasonographically using appropriate views, and with sMRI. Given the limited availability, cost and general anaesthetic risks associated with high-field MRI, more focus should be placed on optimising the ultrasonographic examination. Owners of affected horses should be informed of the guarded prognosis for return to full use.

Navicular Syndrome-related changes to collagen proportion of different cross-sections of the flexor tendons in equine distal forelimb

The aim of this study was to quantify the distribution of aligned and non-aligned collagen in cross-sections of the superficial digital flexor tendon (SDFT) and deep digital flexor tendon (DDFT) in different levels of the distal forelimb of equines diagnosed with NS (Navicular Syndrome). Sixty equine forelimbs were collected. Was compared two groups (NA, Not affected vs. NS-group) by t-Student. Diagnosis of NS was based on clinical and lameness examination, diagnostic analgesia and radiological findings. The proportion of aligned and non-aligned collagens at 2 levels for the SDFT and 3 levels for the DDFT were measured by histochemical stains. The amount of aligned and non-aligned collagen in tendons were calculated using Colour-Based Segmentation function. Regarding collagen, there were significant differences in the amount of aligned collagen (NA: 21.2 ± 1.31; NS-group: 12.2 ± 4.67; p = 0.0026) and non-aligned collagen (NA: 21.8 ± 2.22; NS: 25.1 ± 1.73; p = 0.0241) at the DDFT insertion in the distal phalanx. We concluded that the flexor tendons of the forelimb in equines with NS have different proportions of collagen than those that do not present the diagnosis, indicated by histologically visible increased proportions of non-aligned collagen and decreased of aligned collagen in the extracellular matrix.

Retrospective analysis of lameness localisation in Western Performance Horses: A ten-year review.

Similar to other high-level athletic disciplines, the western performance horse experiences a variety of orthopaedic conditions as a result of rigorous sport-specific physical demands. While musculoskeletal injury rates have been quantified in other equine disciplines, these data are lacking for the western performance athlete. To identify the most common anatomical regions of lameness in western performance horses being evaluated at the nation's largest sanctioned shows over a 10-year study period. Retrospective review of clinical records. Records of diagnostic analgesia of western performance horses competing at nationally sanctioned shows were retrospectively reviewed over a 10-year period to identify affected limb(s) and lameness localisation patterns. A total of 2267 lameness examinations on 2512 horses were included. The average lameness grade was 2.21/5 with 1504/2267 (56%) cases being primarily forelimb in origin while 1173/2267 (44%) were hindlimb related. Forelimb lameness localised to the distal limb in 40% of cases. The proximal metatarsus/distal tarsus was an identified source of lameness in 16% of cases, followed by the stifle in 9% of cases. All-around western performance horses most commonly presented with a single hindlimb lameness (315/1188, 26.5%) in contrast to reining horses that presented with a single forelimb lameness (135/616, 22%). Determining the source of lameness through diagnostic analgesia remains challenging, but the continued assessment of response to diagnostic analgesia may help characterise discipline-specific injuries in western performance horses. Retrospective review of subjective responses to diagnostic analgesia. The distal forelimb and distal tarsus/proximal metatarsus were the two most common anatomical regions of lameness based on response to diagnostic analgesia.

Upper body movement analysis of multiple limb asymmetry in 367 clinically lame horses

Compensatory lameness is common in horses and evaluation can be challenging. To investigate patterns of compensatory movements in clinical cases with fore- or hindlimb lameness before and after diagnostic analgesia. Retrospective clinical study. Multiple limb lameness of 367 horses was characterised by type (push-off, impact or mixed), limb (fore- or hindlimb in predominant lameness) and side (ipsi- or contralateral in concurrent lameness) using a body-mounted inertial sensor (BMIS). Diagnostic analgesia was performed until the percentage improvement of the vector sum in forelimb lameness and the mean difference of the maximum or minimum pelvic height (PDmax or PDmin ) in hindlimb lameness was ≥50%. Linear mixed model and post-estimation of effects were performed by contrast command with multiple comparisons adjusted by Bonferroni method. Correlation of pre- and post-analgesia of all head and pelvis asymmetry parameters was tested with Spearman's rank correlation. Improvement in vector sum per mm after diagnostic analgesia in forelimb impact lameness positively correlated with decrease in PDmax in contralateral mixed lameness (0.187mm, r=.58, P<.05). Improvement in PDmin per mm after diagnostic analgesia in hindlimb mixed and PDmax in hindlimb push-off lameness decreased vector sum in ipsilateral forelimb impact lameness by 0.570 and 0.696mm, respectively (P<.05), with no positive correlation. A variety of cases with inhomogeneous distribution of lameness patterns was investigated retrospectively, therefore, it is impossible to distinguish between true multiple limb lameness and compensatory lameness in this clinical material. Various asymmetry patterns of concurrent lameness were seen in horses with naturally occurring primary forelimb impact lameness with contralateral compensatory hindlimb lameness with a mixed component being the most common. In horses with hindlimb lameness, compensatory movements were seen in ipsilateral forelimbs, mostly as an ipsilateral impact lameness during straight line trot.

CPD article: Radiographic interpretation of the navicular bone: a review

Navicular syndrome (navicular disease) plays a major role in the equine industry as a chronic, degenerative, and often career-limiting disease process, affecting a variety of breeds of horses. In addition to clinical signs and diagnostic analgesia, diagnostic imaging plays a key role in the identification of this disease process; radiography is the most widely used imaging modality. In addition to their clinical utility, foot radiographs are a standard element of most pre-purchase examinations. Good radiographic quality and positioning are necessary for accurate interpretation. Radiographic lesions of the navicular bone, such as sclerosis, enlarged synovial invaginations, distal border fragments and flexor cortical erosions, are important to identify and understand because of their potential role in the disease process. This article reviews an approach to radiological evaluation and interpretation of lesions affecting the navicular bone.

Comparison of lameness outcomes in horses with acute or chronic digital lameness that underwent magnetic resonance imaging

ABSTRACT Aims: To compare the outcome, in terms of lameness score or return to athletic function, of horses with acute vs. chronic digital lameness that underwent magnetic resonance imaging (MRI) of the distal limb and to compare the proportion of horses that received intra-articular therapy of the distal interphalangeal (DIP) joint and pattern of diagnostic analgesia in these groups. Methods: This is a retrospective study of horses (n = 95) with acute (≤12 weeks; n = 46) or chronic (>12 weeks; n = 49) digital lameness that underwent MRI of the distal limb from 2009–2016, at two equine referral centres in the USA. Criteria for inclusion in the study were that a majority of lameness localised distal to the fetlock, and that lameness assessments for ≥12 months following MRI could be obtained from the medical record or the owner could be interviewed regarding their horse's athletic function. Outcome was characterised by an improvement score where 2 = return to work at a previous or higher level or lameness improved by one grade or more, 1 = return to work at a lower level or lameness improved by less than one grade, and 0 = did not return to work or lameness grade worsened. Whether horses had received intra-articular therapy of the DIP joint and the pattern of diagnostic analgesia prior to MRI was also obtained from medical records or by interviewing the owner. Results: There was a difference (p = 0.004) in the proportion of horses assigned to improvement scores of 0, 1 and 2 between horses with acute or chronic lameness. There was no evidence of a difference in the likelihood of having received intra-articular therapy of the DIP joint prior to MRI between horses with chronic or acute lameness (p = 0.085). Similarly, there was no evidence of a difference in the pattern of diagnostic analgesia prior to MRI between the two groups (p = 0.94). Eighty-two percent of owners of horses with acute and 62% of those with horses with chronic lameness had a positive opinion of the utility of MRI as a diagnostic modality. Conclusion: In a population of horses with digital lameness undergoing MRI, a difference in the outcome, in terms of lameness score or return to athletic function was identified between horses with acute lameness compared to those with chronic lameness. Clinical relevance: Horses with digital lameness that undergo MRI when the lameness is acute may have an improved prognosis due to accurate diagnosis and earlier application of appropriate therapy.

Equine scintigraphy: basic principles and interpretation

Bone scintigraphy is the only imaging technique able to demonstrate organ function rather than anatomical details. It involves intravenous injection of a radiopharmaceutical that binds to the bone structures and display alteration in osteoblastic activity. It is commonly used in horses presented for lameness investigation or poor performances, although the sensitivity of the technique in identifying the lesion causing lameness in poor performing sport horses was demonstrated to be low. Conversely, scintigraphy shows high sensitivity in detecting remodelling related to stress-related bone injury and stress fractures, which often occur in racehorses. It must be remembered, however, that the presence of increased radiopharmaceutical uptake does not necessarily indicate a lesion causing pain, and lameness and scintigraphy should be always used in conjunction with in-depth lameness investigation and, when possible, diagnostic analgesia.